Continuous annealing equipment includes a pre-cleaning device and an annealing device (annealing furnace), and a steel strip fed to the continuous annealing equipment is subjected to a pre-cleaning treatment with the pre-cleaning device, followed by an annealing treatment with the annealing device. The pre-cleaning treatment is to remove oil, iron powder, and other substances adhering to the surface of the steel strip. The steel strip subjected to the pre-cleaning treatment is then uniformly oxidized in the annealing treatment to improve the surface quality.
For instance, the pre-cleaning device includes an alkaline immersion tank storing an alkaline solution. Oil adhering to the surface of the steel strip is removed in the alkaline immersion tank (for instance, see Patent Document 1).
Various cleaning solutions (e.g., alkaline solution) used in such a pre-cleaning treatment can effectively clean the steel strip by keeping the temperature of the cleaning solution at a predetermined temperature.